Speedometer.



A. F- POOLE.

SPEEDOMETER. APPUCATHJN man SEPT. 18. mm. RENEWED APR- 2a. 1912.

'Patentd Dec. 4;;1917;

3 SHEETS-SHEET I A. F. POOLE.

SPEEDOMETER. APPLICATION FILED saw. 18. 19:5. nun/5n APR. 23. 1911.

1,249,189. Patented Dec. 4,1917.

3 SHEETS-SHEET 2.

A. F. POOLE.

SPEEDOMETER. V APPLICATIQN FILED 351mm. 1915. RENEWED APR. 23. 1911.

1,249,189. Patented Dec. 4,1917.

I 3 SHEETS-SHET 3.

h i .6 N N m 11 N N an a amen box:

UNITED STATES PATENT ARTHUR F. POOLEOF KENILWORTH, ILLINOIS.

OFFICE.

SPEEDOMETER.

Specification of Letters Patent.

Application filed September 18, 1915, Serial No. 51,402. Renewed April23, 1917. Serial No. 164,027.

To all whom it may concern:

Be it known that I, ARTHUR F. PooLE, of Kenilworth, county of Cook. andState of Illinois, have invented certain new and motion. These and otherobjects of my inthe running gear of the automobile to the Y vention willbe hereinafter described and claimed.

My invention may be best understood by reference to the accompanyingfigures, of which:

V Figure 1 is a sectional view somewhat diagrammatic of the speedometerhead.

Fig. 2 is a diagrammatic view of the pneumatic actuating mechanism whichconnects speedometer head.

Fig. 3 is a side view of the diaphragm at the transmitting end.

Fig. 4. is a modification of the speedometer proper.

Fig. 5 1s a detail of parts of 1.

Figs. 6 and 7 are curves illustrating the way in which the velocity ofthe moving system changes with the time.

Referring to Fig. 2: 10 represents a gear which revolves at a rateproportional to the speed of the moving vehicle or other body travels aroller 13 mounted on a reciprocating bar 1%, which is guided at one endby a fork 15, which straddles a shaft 16, on which 'thegear 11 ismounted. The other end of the bearingl is guided through a sliding'synchronism with it.

bar 17, and is connected to a flexible diaphragm 18, which may be ofleather or other suitable material, Rotation of the gear 11 willtherefore cause the bar lt to reciprocate and with it. the diaphragm 18.This diaphragm serves as a cover for a chamber 19 having a vent 20 towhich is attached a tube 21 communicating withthe speedometer head, inwhich connected to said tube is chamber 22, which latter chamber,however, is of much smaller capacity than the chamber 19. A diaphragm 23serves to close the chamber 22, and connected to this diaphragm is areciprocating rod24 guided in bearings 25 and 26, and on the end 29 :ofwhich are pivoted two links 27 and 28. A'r'atchet wheel 30, having astud 31 mounted thereon, is rotatably mounted in the framework 4.2 ofthe speedometer head. On this stud 31 are pivoted a pair of arms 32,which are connected to thelinks 27 and 28 by the pivots 34 and 35.[A'pawl 36 is pivotally mounted on the arm 32 at 37 and is held in meshwith the ratchet wheel 30 by a spring 38. The arm 33has similarlymountedflon it at 39 a pawl 40, and aspring 41 tends to hold said pawlin contact with the ratchet 30.

From 'the preceding it will be apparent that revolution of the gear 10will cause an oscillation of the rod 14, and that this oscillation, byreason of alternately compressing and exhausting the air contained inthe chambers 19 and 22 and the connecting tube 21, will cause the rod 24to oscillate in Oscillation of this latter rod will produce,,by reasonof the oscillation of the arms 32 and 33, an intermittent rotation ofthe wheel 30, said wheel being advanced one tooth upon the compressionstroke and another tooth upon the exhaust stroke of the rod let.

Inspection of the cam 12 (Fig. 2) discloses that said cam is providedwith a dwell at the end of the compression stroke and also at the end ofthe exhaust stroke, and that the acting surfaces of, this cam are aboutone-third the angular length of the dead portions. This results in thewheel 30 being given a quick feeding motion and then a pause until thenext succeeding motion of the rod 1 1. V

From'the above description of the connections between the front wheel ofthe automobile and the speedometer head proper,

it is obvious that the flexible shaft is re connected by a helicalspring 44 to a negligible, since there is always a larger volume of airexpelled from or drawn into the chamber 19 than is'necessary to work thediaphragm 23 associated with the chamber 22, therefore the rods 14 and24 will move in unison.

I shall now describe the means by which the intermittent rotarymotion ofthe wheel 30, which motion is proportional to the speed to be measured,is transformed into .to whichsaid spring 1S wound, it 1s obvious anapproximately uniform motion, and this uniform motion is measured andtransformed into the indications of a reciprocating hand. The ratchetwheel 30 is mounted in the framework 42 of the speedometer head by meansof a ball bearing 43, and is wheel 45 mounted on a shaft 46, which hasone bearing in the ratchet wheel 30, and the other bearing 48 in thedisk 49 supported rigidly in the framework 42. Mounted in the framework42 by a ball bearing at 50 is a shaft 51 having a pinion 52 rigidtherewith, and adapted to gear with the gear 45.

Mounted on, this shaft 51 is a flywheel 53 and also a conducting disk54. A series of permanent magnets are mounted on the disk '49, and thedisk 54 is placed so as to rotate between thepoles of said magnets. Asis well known, rotation of the disk 54 will induce eddy currentstherein, and said rotation will be resisted with a force proportional toits velocity. The shaft 51 has its upper bearing in the disk 49, andmounted on the end of said. shaft is a permanent magnet 56 having abearing 57 therein which serves as a support of the lower end of a shaft58,011 which is mounted a conducting cup 59. A flange made of mag neticmaterial surrounds the cup 59,. and serves to concentrate the linesof-force of the poles of the magnet 56. The upper bearing of the shaft58 is in the framework;

42. At 61, on the end of the shaft 58, is

mounted the indicating hand 62, which travels over a suitably graduateddial (not shown).

I shall now describe the operation of the indicating parts of thespeedometer head. As before noted, the gear 30 isrotated intermittentlyat a rate which is proportional of thefrequency of the impulses of thediaphragm 18, which latter of course is proportional to the speed to bemeasured. This intermittent rotation of the gear wheel 30 is transmittedby means of the spring 44, the gear wheel 45 and pinion 52 to, the shaft51. Owing to the fact that the rotation of the shaft :51 is resisted wbythe reaction vof said magnet.

gear 0 :uniform in spite of the intermittent nature -of the impulseswhich drive it. The permanent magnet 56 rotates of course 1n unison withthe shaft 51,v and rotation. of. this permanent magnet tends to dragaround with it the conducting cup 59 with aforce that is proportional tothe speed of rotation of This-force is resisted by a spring 63, one. endof which is connectedto the framework and the other end to the shaft 58.Since the; force required to wind up the spring 68 is proportionalto theangle a shaft rotatively mounted in. the bracket 67 mounted on the disk49. Onthe framework 42 is provided a damping chamber 68 having a cover69in .which is the upper bearing of the shaft 66. Two vanes 70. and 71-are rigidly connected to the shaft 66,..andare nearlythe size of thechamber. 68 .inwhich they turn. This .airv damping deviceserves tofurther wipe out any irregularityain the motion of the hand 62 due tothe fact of the motion of the shaft 51 being not exactlyuniform, or dueto any jarwhich may begiven to thehead as a whole.

It will be obvious that theaveragerate of rotation of the shaft 51,and.its attached .magnet 56-.must be exactly the average rate of rotation ofthe ratchet wheel 30, and this equality of rotation will be maintainedindependent of any changes due to friction, or to'the reactionof.thepermanentymag netsv 55 on the conducting disk 54. For if these twospeeds were not exactly equal in the long run,.the spring 44 wouldeitherbe broken through being .wound too tight in case the averagerotation of the ratchetv wheel 30 exceededthe shaft 51, or on the otherhand would not bewoundat all or wound 111 a ,negatlve direction, whichwould correspond to the rotations of the shaft 51 exceeding therotations of the ratchet wheel 30.

lVhile I have shown the indicating means consisting of the permanentmagnet 56 and its .:\.ssociati.11g conducting cup 59 as of the magnetmtype, it 1s obvious that a speed 1n- .dicatlng mechanism of some othertype could be substituted therefor.

In Fig. 4 I have shown .a modification of my device, in which thepermanent magnets 56 and the conducting cup 59 are reversed.

111 this case. apair. Oi-P611369 9? 41439 6 5 712 and 73 are mounted onthe shaft which carries the hand, and instead of a permanent magnetbeing mounted on the shaft 51, a

second conducting disk 74 is mounted there- 1 mounting the ratchet gear30 concentric with the shaft 51 and attaching the spring 44 directly tosaid shaft instead of to shaft 46 as shown in Fig. 1. Also by making thespring 44 sufiiciently long, the system comprising the conducting disk55 and its associated permanent magnets 54 may be dispensed with;However, when the ratchet wheel 80 is connected directly to the shaft 51it is necessary that there be far more pneumatic impulses per mile, thatis, the rod 14 must be reciprocated at a greater rate than is the casein the arrangement I have herein shown. number of impulses per mile fortransmissionand gear up in the speedometer head. It is usual inspeedometers to provide an odometer to record the distance traveled. Ihave not shown an odometer inthis application, since the construction ofthe same is well known to those skilled in the art, and such a one wouldrecognize that the odometer would be very readily geared-to be actuatedfrom either the gear 30 or the rotating shaft 51, since either of theseparts makes a number of revolutions which is proportional to thedistance traveled by the moving vehicle.

Having described the mechanical construction of my invention I shall nowgive the theory of it for the purpose of enabling those skilled in theart to determine the best proportions to give the various elements inorder to construct a speedometer best fitted to the particular speedwhich is to be measured.

Let.I:the moment of inertia of themoving system which in the structureshown, will include the magnet 57, the disk 54, the fly wheel 53 and thegears 45 and 52.

Let Rzthe counter-torque due to the permanent magnets .and it is to beobserved that this torque includes both the torque exerted on the disk54 and also thatexerted on the magnet 56 by the cup 59.

Let T:the instantaneous torque of the spring 44 on the moving system.

Lotti- 1 13116 variable angle of the disk.

I prefer to use a smaller I Let m=the angular velocity of the disk. Lett:the time.

The motion of the disk is determined by 5 three torques, (1) the changeof momentum (2) the counter-torque of the magnetic field, which asabovenoted is proportional to'the velocity of the clisk and is equal to andthird, the force of the spring which is proportional to the anglebetween the disk and the wound end of the spring=K (flt) where K is theconstant of the spring, 6

is the angle of the lower end, and is that of the upper end.

Equating these torques At this point it will be convenient to write andb =T Substitute these values in equation (1) and rearrange the terms.

It is to be noted at this point that the solu tion of this diflerentialequation is the same as the solution of the equation of motion of aballistic galvanometer or the equation of any body which is moving underthe influence'of an acceleration which varies'directly as thedisplacement from the zero point and encounters a resistance which isproportional to the velocity.

The solution of this differential equation is well known and is in twoparts, the particular integral, 5=6, and the complementary functionwhich is the solution of the left hand member equated to zero where m,and m are the roots of the equation m +2am+b :0 from which m a+ /a .-bThe complete solution of the differential equation is therefore 1. Wherethe roots m and we, are both real and equal to each other. I Then 2.Wherethe roots m andm arereal and tqi s not' equalto each "other inwhich case the equation takes: the form A and B being arbitraryconstants to be determined from the initial condition.

3. In case the values we, and m are imaginary, the arbitrary constants Aand B becon'ie imaginary also and then by a-proper substitution of theexponential values of the sine and cosine the equation may betransformed into where A and a are integration constants determined fromthe initial conditions.

f-IIlFlgS.' 6 and 7 I have shown some curves computed on the assumptionof concrete values for the constants R, K and I, assuming that theperiod of wind occurs once every two seconds and that the amount of windis equal to one radianas referredto the shaft 51, these values beingpurely arbitrary and being assumed simp'ly'to illustrate the way inwhich the vvelocity of the moving system changes with the time. Thecurves were computed onthe assumption that the system started rest andthen the velocity at the end of two seconds was found, intermediatevalues being also computed to give the intermediate points on the curve.The equation for the velocity may be obtained by direct differentiationof the equation for 52$. At the end of'two seconds the system had acertain velocity (0 and had turned a certain angle e from Zero. Startingwith these new values ;of the velocity and the angle new constants weredetermined for the differential equation and the change in velocity wascomputed for an additional period of two seconds. Continuing thisprocess for about eight periods of two seconds each or thatcorresponding to a lapsed time of sixteen seconds. gives the data fromwhich the curve of Fig. 7 was drawn. Inspection of this figure-showsthat the velocity has become practically uniform, that is the velocityat the beginning of an epoch is the same as the velocity at the end ofthe epoch and this velocity starts in below the mean value and extendsabove it, then returns below the mean value again so that the averagevelocity is equal to the average velocity of the wound' end ofthespring.

The curve of Fig. 7 was computed according to the same method but withthe constants 11:9, K:2 and I:9.

In this 'case the departure from the mean velocity after things havereached a steady state is 'seen to be much less than with the constantsshown in Fig. =6. This is to be expected'since increasing the moment ofinertia of the system will tend to smooth the ripples in the curve. pThecdflicirit i Of damping-{and t m" *cient of the' spring may bereadily found in any.=givenstructure by disconnecting gears 45 and 52and fastening the shaft 58 so that it will not turn in its bearing. Themoving system mounted on the shaft 51 is then deflected through an angleand its time of vibration and amplitude of successive oscillations arenoted. A weight of known moment of inertia is then placed on the axis53, the system vibrated a' second time and similar observations made.From these two ob- 'servations the constants required maybe readilydetermined, the formulas for so doing having already been-worked out forsimllar constants in the case of determining the in tensity of theearths magnetic field by the 'method of vibrating a magnet therein.

I do not wish to be limited to the precise arrangement herein shownsince I claim:

1. In combination a rotating member driven intermlttently, a secondmember adapted to revolve agalnst a resistance which varies as thevelocity, and elastic means connecting the two members whereby theintermittently moving member drives the second one.

'2. In combination a member adapted to be rotated, means forintermittently driving the same, a second member adapted to be rotated,a magnetic damping resistance and anelastic member connecting the saidtwo members adapted to be rotated.

- 8. In combination a rotatable member, means for-intermittently drivingthe same, a second rotatable member, a magnetic damping-resistanceoperative on said second member and a spring connecting said twomembers.

4. In a speedometer the combination of means for obtaining a series ofintermittent second rotatable member, a magnetic damping resistancetending to prevent the rotation of said second member, a springconnecting the two said rotatable members, and means for measuring thespeed of rotation of said'second member. "6. In 'combmatlon a rotatablemember means for intermittently rotating same, a

second ro-tatablemember, a magnetic damping resistance tending toprevent the rotation of said second member, a spring con-' nectingthetwo said rotatable members, and magnetic means formeasuring the speed ofsaid second rotating member.

7. In combination a rotatable member, means for said-membenstep by step,

means for translating the intermittent motion of said member in anapproximately uniform motion of a second member and means to measure thespeed of rotation of said second member.

8. In combination a rotatable member, means for driving said member,step by step, a second rotatable member, means for translating theintermittent motion of said first member into an approximately uniformmotion of said second member and magnetic means to measure the rotationof said second member.

9. In combination a rotatable member, means for driving the same step bystep, a conductor, a magnetic field, means to translate the step by stepmotion of said first member into an approximately uniform relativemotion of said conductor and said magnetic field and means to measurethe speed of relative moment between said conductor and said magneticfield.

10. In combination a rotatable member, means for intermittently drivingthe same, a magnet, magnetic means for translating said intermittentmotion of the first memher into an approximately uniform rotation ofsaid magnet, an electric conductor adapted to be displaced by therotating of said magnet and means for indicating the amount of saiddisplacement.

11. In a speed indicating apparatus, means for producing a succession ofintermittent impulses proportional to the speed to be measured, meansfor translating said impulses into a step by step motion of a rotatablebody, means for translating said step by step motion into anapproximately uniform motion of a magnetic field, a conductor adapted tobe acted on by said magnetic field, a spring to hold said conductor in anormal position and means to indicate the displacement of said conductorfrom its normal position.

12. In a combination a rotatable electric .conductor rotatable in astationary magnetic field, a second magnetic field rotatable with saidconductor, a second conductor adapted to be displaced by said secondmagnetic field and means to indicate the amount of displacement of saidsecond conductor.

18. In a speed indicating apparatus, the combination of means to producea series of pneumatic impulses varying as the speed to be measured, arotatable member, means to translate said impulses into a step by stepmotion of said rotatable member, a second rotatable member, a magneticresistance to govern the rotation of the same and an elastic connectingmeans between said first and second rotatable members.

14:- In a speed indicating apparatus, the combination of means toproduce a series of pneumatic impulses varying as the speed to bemeasured, a rotatable member, means to translate said impulses into astep by step motion of said rotatable member, a second rotatable member,a magnetic resistance to govern the rotation of the same, an elasticconnecting means between said first and second members and means tomeasure the speed of rotation of said second rotatable member.

15. In a speed indicating apparatus, the combination of means to producea series of pneumatic impulses varying as the speed to be measured, arotatable member, means to translate said impulses into a step by stepmotion of said rotatable member, a second rotatable member, a magneticresistance to govern the rotation of same, an elastic connecting meansbetween said first and second members and magnetic means to indicate thespeed of said second rotatable member.

16. In an automobile speedometer, the combination of means to produce aseries of pneumatic impulses varying as the speed to be measured, saidmeans to be located on the running gear of the automobile, a flexibletube connecting said means to a mechanism for translating said series ofimpulses into intermittent rotation of a revoluble member, a springconnecting said member to a second member, said second member beingsubject to a resistance varying as the speed of rotation of said member,and means to indicate the speed of said second member.

17. In an automobile speedometer, the combination of means to produce aseries of pneumatic impulses varying as the speed to be measured, saidmeans to be located on the running gear of the automobile, a flexibletube connecting said means to a mechanism for translating said series ofimpulses into intermittent rotation of a revoluble member, a springconnecting said member to a second member, said second member beingsubject to a resistance varying as the speed of rotation of said member,and magnetic means to indicate the speed of said second member. I

In witness whereof I have hereunto signed my name this 17th day of Sept,1915.

ARTHUR F. POOLE.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. G.

